The present invention relates to ascertaining the miss distance of firing upon stationary or moving training targets, under utilization of the compression or shock waves of passing projectiles, whereby particularly the method as well as equipment for carrying out the method is the subject matter of the invention.
It is known generally to measure acoustically the distance by which a projectile aimed at a target either a resting i.e. a stationary target or a moving training target, has missed it. The target may have moved with subsonic speed. Projectile aimed at a target usually moves with supersonic speed and produces a conically spreading shockwave. This shockwave and its passage is detected at measuring points under utilization of microphones. The pressure and shock wave production point as far as the projectile path is concerned as well as the amplitude and/or the duration of the shockwave is used for measuring the miss distance. This method of measuring the distance is however not very reliable for moving targets particularly on account of the vector relation between the projectile speed, the target speed and the shockwave as it propagates. In fact, a correct result will be ascertained only in cases of peculiar coincidences among these vectors.
German printed patent application 31 22 644 discloses a method and equipment for acoustically measuring the miss distance as between a projectile and a flying target, and attempts have been made as per this reference to avoid the errors outlined above. Specifically, the method as disclosed there attempts to measure the strength of the shockwave pressure produced by the passing projectile which measurement is carried out by the target itself and the measuring result is transmitted to equipment on ground.
Based on predetermined parameters the distance between projectile path and target is ascertained at the instant of passage which in effect is the shortest distance between target and projectile. This obtains by ascertaining the period of duration of the pressure wave as it affects the target, and the angle between target trajectory and projectile trajectory. These values are then used to calculate the true distance between target and trajectory under utilization of a correcting factor. The accuracy of the measurement is dependent on the accuracy of predetermined parameters. Since a pressure wave is measured by means of microphone the so called "bang" effect influences the measurement and it is well known that problems arise when pressure by means of microphones.
European patent 0003095 suggests an expansion of the method mentioned above but now under utilization of five microphones whereby 4 microphones are arranged in the corners of a polyhydron or "tetra" This arrangement permits not only the quantitative measurement of space and distance information between projectile path and target but the directional information is also available in this way. However, this method is subject to the following problems.
The configuration of the pressure or compresssion shock wave produced by the passing projectile is dependent on numerous operating parameters such as the type and configuration of the projectile, its distance, target speed and angle of directing the projectile so that any kind of combination requires separate calibration; numerous parameters enter into the picture and the situation is quite difficult. The same is true with regard to the correction needed for and in the evaluation by means of processing equipment during real time operation. On the other hand it has to be considered that changes in the configuration of the pressure wave as it spreads is very difficult to ascertain by way of calculation so that an evaluation requires numerous very extensive and expensive calibrating procedures, for obtaining particular wave contours as reference under various different conditions of operation; also, there is a need for cyclically repeated calibration.
The ascertaining of the pressure wave configuration by means of a microphone is interfered with through a large number of interfering sources such as noise, temperature variations and particularly the case of relatively high target speeds, these factors become increasingly noticeable. Also, the conversion of information under consideration of the Doppler effect and certain properties of the microphone are difficult.